1. Field of the Invention
The present invention relates to methods and apparatus for providing a non-circular steering wheel assembly and airbag modules suitable for use with non-circular steering wheels. More specifically, the present invention relates to non-circular steering wheel designs and to airbag housings, cushions and airbag modules for use in vehicles using non-circular steering wheels.
2. Description of Related Art
Safety belts are designed to protect the occupants of a vehicle during events such as automobile collisions. In low-speed collisions, the occupants are generally protected from impact with objects located inside the vehicle such as the windshield, the instrument panel, a door, the side windows, or the steering wheel by the action of the safety belt. In more severe collisions, however, even belted occupants may experience an impact with the car's interior. Airbag systems were developed to supplement conventional safety belts by deploying into the space between an occupant and an interior object or surface in the vehicle during a collision event. The airbag acts to decelerate the occupant, thus reducing the chances of injury to the occupant caused by contact with the vehicle's interior.
Many typical airbag systems consist of several individual components joined to form an operational airbag module. Such components generally include an airbag cushion, an airbag inflator, a sensor, and an electronic control unit. Airbag cushions are typically made of a thin, durable fabric that is folded to fit into a compartment of a steering wheel, dashboard, interior compartment, roof, roof rail, roof compartment, or other space in a vehicle. The airbag inflator is in fluid communication with the airbag cushion, and is configured to produce a gas to inflate the cushion when it is needed. The sensors detect sudden decelerations of the vehicle that are characteristic of an impact. The readings taken by the sensors are processed in the electronic control unit using an algorithm to determine whether a collision has occurred.
Upon detection of an impact of sufficient severity, the control unit sends an electrical signal to the inflator. The inflator uses one of many technologies, including pyrotechnic compounds and pressurized gas, to produce a volume of an inflation gas. The inflation gas is channeled into the airbag, inflating it. Inflation of the airbag causes it to deploy, placing it in a position to receive the impact of a vehicle occupant. After contact of the occupant with the airbag and the corresponding deceleration of the occupant, the airbag rapidly deflates. To accomplish this, the inflation gas is vented from openings in the airbag, deflating it and freeing the occupant to exit the vehicle.
As experience in the manufacture and use of airbags has increased, the engineering challenges involved in their design, construction, and use have become better understood. Most airbag systems are designed to rapidly inflate and provide a cushion in proximity to a vehicle occupant. Many such cushions are configured to be placed in front of a vehicle occupant. Placement of the cushions is determined based on presumptions made of the position of a vehicle occupant during normal operation of the vehicle. Thus, a vehicle occupant enjoys optimal protection from a specific airbag when the occupant is in the presumed range of positions when the airbag deploys.
In some situations, injuries have been noted to occur when the occupant is “out of position” with regard to the presumed position discussed above. Injuries similar to out of position injuries may also result from improper deployment of the airbag. Improper deployment may result in either poor placement of the cushion when contacted by a vehicle occupant or incursion of the airbag cushion into the space reserved for the vehicle occupant. Such incursion during deployment may raise the probability of injury to the vehicle occupant.
Automotive engineers have begun to incorporate “drive-by-wire” technologies into newer vehicles. These technologies eliminate a mechanical connection between the driver and a system of the vehicle by receiving and interpreting a driver's manual commands and electronically implementing them. One currently available example of this technology intervenes by receiving a driver's inputs from the accelerator pedal of a vehicle, interpreting them, and automatically adjusting the throttle in response.
Some drive-by-wire technologies are envisioned for use in the steering mechanisms of a vehicle. The use of some drive-by-wire steering systems would allow vehicle designers to replace the standard circular steering wheel used in most cars today with a non-circular design. Such non-circular designs often take a rectangular form similar to the geometries of currently-used aircraft steering apparatus. This design presents several safety engineering challenges left unaddressed by current airbag designs and configurations.
A first challenge is presented by the fact that the function of current steering wheel-mounted airbag cushions is generally reliant on the presence of a circular steering wheel. More specifically, commonly-used cushions have a substantially circular shape which overlaps the steering wheel when inflated. The steering wheel-facing surface of the airbag cushion abuts the surface of the steering wheel when inflated and contacts the surface of the steering wheel when an occupant strikes the cushion. The steering wheel provides a reaction force to the airbag cushion, supporting it.
When a steering wheel has a non-circular shape, however, the steering wheel may not be able to provide sufficient support to the cushion. In one example, when the steering wheel has a flattened-rectangular geometry similar to that used in aircraft, the use of a generally circular airbag cushion is problematic because the cushion has no reaction surface at the 12:00 and 6:00 positions. The application of a load to the occupant-facing portion of the cushion could cause the cushion to fold.
Accordingly, a need exists for non-circular steering wheel designs and for airbag housings, cushions and modules for use in vehicles using non-circular steering wheels. Such non-circular steering wheel designs and airbag module housings, airbag cushion designs and airbag modules for use in vehicles using non-circular steering wheel designs are provided herein.